Scratch resistant thermoplastic article

ABSTRACT

A process and resulting thermoplastic article is provided suitable for use in constructing furniture. The thermoplastic article contains hardened particulates such as powders of alumina oxide which brings about an improved cut and scratch resistance to the surface of the articles. The hardened particulates may be integrally mixed with the extruded product or applied post-molding to a surface of the shaped article.

FIELD OF THE INVENTION

[0001] This invention is directed towards a process and the resulting product of an extruded thermoplastic sheet or a molded thermoplastic article having improved abrasion resistance and scratch-resistant properties. The improved properties are achieved by the addition of a plurality of particles of a hardened substrate, such as aluminum oxide, which may be incorporated into the thermoplastic material. The particulate additive imparts greater wear resistance and scratch resistance to the thermoplastic structure.

BACKGROUND OF THE INVENTION

[0002] Thermoplastic materials are widely used as a material for articles of manufacture. For instance, it is known in the art to use thermoplastic polyvinyl chloride (PVC) to mold articles of furniture such as chair frames and other furniture articles. The PVC resin is often provided with an integral wood grain finish to simulate the appearance of real wood. While thermoplastic polymer sheets and profiles offer high impact resistance, the wear resistance and abrasion resistance is low.

[0003] It is also known to apply decorative films, papers, and surface polymer layers to the laminated structure to improve the appearance of the product. However, such overlayments are often thin and hence prone to damage and are not easily repaired.

[0004] U.S. Pat. No. 6,106,654 provides a thermoset laminate in which a paper web impregnated with melamine-formaldehyde resin is applied as a surface layer to the laminate. The sheet is coated with the impregnated paper, one side of the paper containing aluminum oxide particles.

[0005] U.S. Pat. No. 5,763,048 discloses a PVC substrate having a protective layer of a cured resin having polycarbonate particles mixed with the resin. The resin is cured by applying ionizing radiation to the PVC substrate.

[0006] U.S. Pat. No. 4,921,669 discloses scratch resistant coatings suitable for use with a PVC substrate in which a separate coating of a monomer mixture is applied to the PVC surface by polymerization. The monomer has a high cross-linking density and provides good scratch resistance.

[0007] While there are a variety of scratch resistant coatings and resins known within the art, there remains room for improvement and variation.

SUMMARY OF THE INVENTION

[0008] It is one aspect of one of the present embodiments to provide for an extruded thermoplastic polymer which incorporates an effective amount of a particulate additive such as aluminum oxide, the particulate additive providing scratch resistance and wear resistance to the extruded polymer.

[0009] It is yet another aspect of at least one of the present embodiments to provide a process of incorporating an effective amount of a hardened particulate which is incorporated directly into the thermoplastic polymer during the compounding of the polymer and prior to extrusion.

[0010] It is yet another aspect of at least one of the present embodiments to provide a process of providing an extruded thermoplastic polymer in which an effective amount of a particulate additive is incorporated into a polymer extruding step.

[0011] It is yet an additional aspect of at least one of the present embodiments to provide a molded thermoplastic polymer containing between about 1% to about 10% by weight of an inorganic filler selected from the group consisting of silicate, silica oxide, fumed silicas, alumina, aluminum oxide, ceramics, and combinations thereof, and having a particle diameter of about 4 to about 10 microns.

[0012] It is another aspect of at least one of the present embodiments to provide a thermoplastic sheet or extrusion molded profile in which particulates are embedded into a surface of the sheet by pressure application of the particulates into the softened sheet surface.

[0013] It is yet another aspect of at least one of the present embodiments to provide a process of providing a scratch resistant coating to a thermoplastic extrusion product comprising the steps of: providing a thermoplastic extruded product having a surface temperature heated to a softening temperature; applying an effective amount of a particulate, the particulate being applied at a concentration of about 1 to about 25 grams per square meter; mechanically pressing the particulate into the surface of the extruded product using a pressure of about 150 to about 200 pounds per linear inch; and allowing the thermoplastic material and pressed particles to cool.

[0014] It is yet another aspect of at least one of the present embodiments to provide a thermoplastic extruded sheet having a scratch resistant surface comprising the steps of providing a thermoplastic extruded sheet; embossing a surface of said thermoplastic sheet, thereby imparting a matte finish to the sheet, the matte finish comprising a series of surface elevations and depressions; warming the matte surface to a softening temperature; applying a plurality of particulates onto the matte surface; and applying pressure to the matte surface and the particulates, thereby embedding the particulates into the matte surface.

[0015] It is yet another aspect of at least one of the present embodiments to provide a thermoplastic article comprising a molded thermoplastic panel, the panel having an upper surface, a lower surface, and four edges; a plurality of particulates selected from the group consisting of silicas, silica oxides, fumed silicas, alumina, alumina oxides, ceramics, and combinations thereof, the plurality of particulates positioned within at least a portion of the panel which includes at least one of the upper surface or the lower surface; wherein, the plurality of particulates improves the scratch resistance of at least one of the upper surface or the lower surface.

[0016] The sheets, panels, and other articles made in accordance with the present invention are useful in a variety of hard-wearing surface applications. Such applications include, but are not limited to, counter tops, flooring, and commercial or residential furniture items.

[0017] These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] A full and enabling disclosure of the present invention, including the best mode thereof, to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying drawings.

[0019]FIG. 1 is a perspective view of one embodiment of thermoplastic sheet made in accordance with the present invention.

[0020]FIG. 2 is an alternative embodiment of a thermoplastic sheet made in accordance with the present invention.

[0021]FIG. 3 is a third alternative embodiment setting forth a thermoplastic sheet having an embossed surface made in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0022] Reference now will be made in detail to the embodiments of the invention, one or more examples of which are set forth below. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment, can be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention cover such modifications and variations as come within the scope of the appended claims and their equivalents. Other objects, features, and aspects of the present invention are disclosed in the following detailed description. It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only and is not intended as limiting the broader aspects of the present invention, which broader aspects are embodied in the exemplary constructions.

[0023] In describing the various figures herein, the same reference numbers may be used throughout to describe the same material, apparatus or process pathway. To avoid redundancy, detailed descriptions of much of the apparatus once described in relation to a figure is not repeated in the descriptions of subsequent figures, although such apparatus or process is labeled with the same reference numbers.

[0024] As best seen in reference to FIG. 1, a first embodiment of one of the present inventions is set forth. An extruded article, seen here as a thermoplastic extruded PVC sheet 10 is provided. Contained within the sheet are a plurality of particles 20 such as aluminum oxide particles. The particles may be in a granular form, preferably have high hardness values, and typically have a roughly spherical shape. However, other shapes of particles as well as variations in particle sizes may be used and which will offer satisfactory results. Suitable hardened particles include particulates of silica, silica oxides, fumed silicas, alumina, aluminum oxides, various ceramic materials, and combinations thereof which possess high strength and high abrasion resistant properties.

[0025] The size and/or diameter of the particulates is not believed critical with respect to the present invention. In accordance with this invention, it has been found that a particle size of between about 4 to about 10 microns (1000 to 1200 grit) for aluminum oxide (Reade Advanced Materials) have been found to impart good scratch resistance and wear properties to the thermoplastic extrusion product 10 when present in a concentration of between about 1% to about 10% by weight. As a general rule, increasing the amount of hardened particles within the thermoplastic material increases the cut and scratch resistance and abrasion resistance of the resulting thermoplastic molded article. Alternatively, concentrating the amount of particulates present along at least one surface region of the molded article as described below, also brings about beneficial improvements in the wear properties and scratch resistance of the extruded sheet or molded article. Larger or smaller average sized particulates may also be used.

[0026] In addition to PVC, other suitable thermoplastic resins may be used to form extruded or molded thermoplastic articles. Such thermoplastic materials include styrene-based polymers, olefins, polyamides, and similar materials which are well known within the art.

[0027] A thermoplastic article as set forth in FIG. 1 may be made by incorporating the particulates directly into the thermoplastic polymer. The particulates may be added during the compounding stage prior to the polymer extrusion. Alternatively, a dosing screw or other metering device may be used to introduce the hardened particles directly to the extruder. Nonetheless, in either event, the thermoplastic article contains a plurality of particulates which are distributed throughout the polymer material.

[0028] As seen in reference to FIG. 2, an alternative embodiment of a thermoplastic article may be seen in reference to a thermoplastic sheet of PVC 110. A coating of particulates 120 is applied to the surface of the molten sheet as the molten sheet exits the extruder die. The particulates may be applied by a pneumatic sprayer, a mechanical duster, or through an electrostatic disbursion. The particulates are applied at a concentration of between about 1 to about 25 grams per square meter. When so disbursed, the particulates make contact with the surface of the molten sheet. When applied prior to cooling of the molten sheet, the particulates may be mechanically pressed into the upper molten polymer layer by an application of pressure. Suitable pressure may be applied using nip rollers or the use of a vacuum pressure against a platen. A pressure roller, nip roller, or calendaring roll may be used to apply a pressure of about 150 to about 200 pounds per linear inch to sheet extrusion product. Vacuum pressure may be used in the case of article profiles which are not suitable for passing through pressure type rollers. Following the pressure application of the particulates into the molten surface of the thermoplastic material, the subsequently impregnated sheet or profile is then cooled as is conventional within the art.

[0029] It is also possible to apply the particulates to the surface of the thermoplastic material following the initial production of the article. In such instances, the previously formed thermoplastic sheet or profile is heated to a surface softening temperature and the particulates are then applied to the surface of the article as described above. Following application, the mechanical pressure is applied as described above. If desired, the particulates may also be heated to a temperature greater than the softening temperature of the thermoplastic polymer prior to application. In so doing, the particulates may more readily adhere to the surfaces to be coated.

[0030] A third embodiment of the present invention is seen in reference to FIG. 3. FIG. 3 sets forth a molded thermoplastic article as seen in the form of an extruded sheet 210. A surface of the extruded sheet is embossed using a conventional embossing roller which creates a matte effect to the sheet. The embossing roller places a series of raised surfaces 112 and depressions 114 along the sheet surface. Following embossing, the matte surface of the sheet is raised to a softening temperature whereupon the desired concentration of hardened particles 220 is applied and then pressed into the surface of the sheet. As best seen in reference to FIG. 3, the elevated ridges 212, along with the other surface regions, become coated with a pressed layer of particulates. As a result, the surface now defines a region containing a number of particulates which impart excellent abrasion and scratch resistant properties to the molded article. Further, the matte-like surface of the alternating elevated regions and depressions serve to minimize the appearance of scratches and other surface imperfections which may occur.

[0031] In addition, as set forth in detail in Example 1 below, it is also possible to coat or otherwise introduce the particulate additive to the extruded sheet prior to a subsequent surface embossing step.

[0032] The thermoplastic, surface hardened materials are particularly well suited for use in constructing furniture from the thermoplastic laminates. For instance, a thermoplastic PVC resin may be provided in which a simulated wood grain appearance is created by the use of pigments mixed in with the PVC resin. The PVC pigmented resin provides an attractive wood grain appearance to the resulting molded furniture article. By incorporating particulates within the thermoplastic material and more particularly by placing a surface layer of hardened particulates along the surfaces of the thermoplastic molded article, the surface finish has improved resistance to cuts and scratches. When used in materials such as a pigmented thermoplastic article, the hardened particulates do not alter or detract from the desired pigmentation of the extruded product.

[0033] The thickness of the PVC or other thermoplastic polymer products may be varied depending upon the capabilities of the extrusion equipment and the desired end use. With respect to making articles of furniture and thermoplastic panels which may be used in the construction of furniture, a PVC thickness of about 2 mm is sufficient. One way of making panels and various articles of furniture using wood grained PVC can be found in relation to Applicant's copending application having Ser. No. 09/656,281 filed on Sep. 6, 2000, and which is incorporated herein by reference in its entirety. In reference to the incorporated disclosure, the extruded PVC article may be modified according to the present invention to have an effective amount of the particulates. Such particulates may be mixed uniformly throughout the extruded PVC article or may be applied to one or more of the exterior surfaces of the article. As discussed above, one or more surfaces of the PVC article may be embossed which further minimizes the appearance of scratches and allows a coating of the scratch-resistant particulates to be applied to the embossed surface and to the immediately adjacent region of the thermoplastic material.

[0034] It is also envisioned that the wear-resistant and scratch-resistant thermoplastic polymer sheets described herein may also be used as the wear surface of a flooring composite material. The thermoplastic sheets may be molded and cut to desired shapes and thicknesses and may be optionally secured to other substrates so as to render a composite material suitable for use as a flooring material, stair treads, or other similar articles designed for high wear applications.

[0035] Articles made in accordance with the present invention were evaluated according to test standards set forth in NEMA Standards Publication LD 3-2000 and which are incorporated herein by reference. In all instances, the inclusion of the particulates in the thermoplastic article brings about an improvement in the resistance to abrasions, cuts and scratches. Additional details of construction may be found in reference to Example 1 below.

EXAMPLE 1

[0036] A high impact, thermoplastic wood-grain polyvinyl chloride sheet was extruded from a 60-inch sheet die set at a 2.8 mm thickness. As the extruded thermoplastic sheet exited the extruder, a coating of aluminum oxide particulate was electrostatically applied onto the top of the sheet at a concentration of 20 grams/meter². The aluminum oxide had an average particle size of between about 4 to about 10 microns.

[0037] The molten PVC sheet, coated with the aluminum oxide particles, is passed through embossed calendaring rollers at a pressure of about 150 pounds per linear inch. The gap between the rollers was set at 2.4 mm in thickness. The resultant embossed sheet was cooled and tested for abrasion resistance using Wear-Resistant Test 3.13 and the Linear Glass Scratch-Resistance Test 3.7 as set forth in the NEMA Publication LD 3-2000.

[0038] The wear-resistance procedure 3.13 uses sand paper placed on abrader wheels to determine resistance to abrasive wear through. Using the evaluation apparatus and materials set forth in the NEMA 3.13 publication, a wear-resistance of 3,200 cycles is obtained which exceeds NEMA specifications for a high wear substrate.

[0039] Test method 3.7 was also used to determine linear glass scratch resistance of the coated sheet surface. Test method 3.7 uses a scratch tool having a sharpness and hardness similar to silica. The scratch resistance of the above described sheet was determined to be 150 grams with the product sample having a tristimulus Y value (lightness) of 30. These values represent a high scratch resistant property for the evaluated thermoplastic sheet.

[0040] Control samples of extruded PVC lacking the aluminum oxide particulates fail to achieve the NEMA standards for high wear resistance and exhibit poor scratch resistant values.

[0041] Although preferred embodiments of the invention have been described using specific terms, devices, and methods, such description is for illustrative purposes only. The words used are words of description rather than of limitation. It is to be understood that changes and variations may be made by those of ordinary skill in the art without departing from the spirit or the scope of the present invention, which is set forth in the following claims. In addition, it should be understood that aspects of the various embodiments may be interchanged, both in whole or in part. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained therein. 

That which is claimed is:
 1. A process of providing a wear resistant coating to a thermoplastic article comprising the steps of: providing a thermoplastic article having a surface temperature heated to a softening temperature; applying an effective amount of a particulate to a surface of the article, said particulate imparting wear resistant properties to the surface of the thermoplastic article, mechanically pressing the particulate-containing surface with a pressure of about 150 to about 200 pounds per linear inch; and allowing said thermoplastic article to cool.
 2. The process according to claim 1 wherein said step of applying an effective amount of a particulate further comprises supplying said particulate at a concentration of about 1 to about 25 grams per square meter.
 3. The process according to claim 1 wherein said particulate is selected from the group consisting of silicates, silica oxide, fumed silica, alumina, alumina oxides, ceramics, and combinations thereof.
 4. The process according to claim 1 wherein said particulate has an average particle diameter of between about 4 to about 10 microns.
 5. The process of forming a thermoplastic extruded sheet having a wear resistant surface comprising the steps of: providing a thermoplastic sheet; embossing a surface of said thermoplastic sheet, thereby imparting a matte finish to the sheet, the matte finish comprising a series of elevations and depressions; warming the matte surface to a softening temperature; applying a plurality of hardened particulates onto the matte surface; and applying pressure to the matte surface and the particulates, thereby embedding the particulates into the matte surface.
 6. The process according to claim 5 wherein said step of applying an effective amount of a particulate further comprises supplying said particulate at a concentration of about 1 to about 25 grams per square meter.
 7. The process according to claim 5 wherein said particulate is selected from the group consisting of silicates, silica oxide, fumed silica, alumina, alumina oxides, ceramics, and combinations thereof.
 8. The process according to claim 5 wherein said particulates have an average particle diameter of between about 4 to about 10 microns.
 9. The process according to claim 5 wherein said step of applying pressure further includes applying a pressure of between about 150 to about 200 pounds per linear inch.
 10. A process of providing a thermoplastic extrusion product comprising the steps of: compounding a thermoplastic polymer selected from the group consisting of polyvinyl chloride, styrene-based polymers, olefins, and polyamides; introducing into said thermoplastic resin in at least one of a compounding step or an extruding step an effective amount of a particulate; extruding said thermoplastic polymer; molding said thermoplastic polymer into a desired shape; wherein said particulate additives increases wear resistance and cut resistance of the thermoplastic article.
 11. The process according to claim 10 wherein said step of applying an effective amount of a particulate further comprises supplying said particulate at a concentration of about 1 to about 25 grams per square meter.
 12. The process according to claim 10 wherein said particulate is selected from the group consisting of silicates, silica oxide, fumed silica, alumina, alumina oxides, ceramics, and combinations thereof.
 13. The process according to claim 10 wherein said particulates have an average particle diameter of between about 4 to about 10 microns.
 14. A thermoplastic article comprising: a molded thermoplastic panel, said panel having an upper surface, a lower surface, and four edges; a plurality of particulates selected from the group consisting of silicas, silica oxides, fumed silicas, alumina, alumina oxides, ceramics, and combinations thereof, said plurality of particulates positioned within at least a portion of said panel which includes at least one of said upper surface or said lower surface; wherein, said plurality of particulates improves the wear resistance of said at least one of said upper surface or said lower surface.
 15. The thermoplastic article according to claim 14 wherein said plurality of particulates is concentrated along a surface region of at least one of said upper surface or said lower surface.
 16. The thermoplastic article according to claim 14 wherein an upper surface of said panel is embossed, said embossed surface further engaging said plurality of particulates.
 17. The thermoplastic article according to claim 15 wherein said plurality of particulates are present in a concentration of between about 1 to about 25 grams per square meter of said surface region.
 18. The thermoplastic article according to claim 16 wherein said embossed surface further defines a concentration of said hardened particulates, said particles present in a concentration of between about 1 to about 25 grams per square meter.
 19. The thermoplastic article according to claim 14 wherein said plurality of particulates is present in said thermoplastic panel in a concentration of between about 1% to about 10% by weight. 